Spark plug



March 17, 1925.

W. C. THOMA SPARK PLUG Filed Sept. 27, 1921 Patented Mar. 17, 1925.

WILLIAM CHRIS THOMA, QF LAURENS, IOWA.

SPARK PLUG.

Application filed September 27, 1921.

T0 all-whom c't may concern Be it known that 1, WILLIAM CHRIS T-HOMA,acitizen of the United'States, and

V resident of Laurens, inthe county of Pocahontas and State of Iowa,have invented a certain new and useful Spark Plug, ofwhich the followingis a specification.

This invention relates to improvements in sparkplugsin which theinsulating member is'atorined of a series of transverse layers of micaor similar insulating material bound together'by means-of longitudinallyextending rods. Insulating members constructed in thismanner areVlyefilclellll as long as the edges of thelayers are-kept free from oil,but when the insulators are used in cylinders in which a considerableamount of oil is used, the spaces between thelayersbecome saturated withoil and shortcircuiting results be tween the longitudinally extendingterminal member andthe casing of the spark plug in which theinsulatoris-mounted. This is due to the tact that-the space'between thelayers of mica become filled with conducting substances which enter thespaces between the discs or layers of material.

One of the objects of my invention is to overcome the above difficultyby providing means whereby the-cylindrical face of the insulating membermay be absolutely protected against oil from coming into engagementtherewith.

A further object is to provide in a spark plug having an insulatingmember formed of a series of adjacent discs of insulating material, newand improved means for mounting the insulating member within the casingof the spark plug in such a manner that the circumferential edges of thediscs will not be exposed to oil or similar substances.

A further object is to provide in a spark plug improved arrangement ofspark terminals and the manner in mounting the same.

A still further object is to provide improved means for mounting theinsulating member within the casing of a spark plug.

These and other-objects will'be apparent to those skilled in the art.

My invention consists in-the construction, arrangement and combinationof the various parts of the device whereby the objects contemplated areattained, as hereinafter more fully set forth, pointed out in anyclaims,

Serial No. 503,637.

and illustrated in the accompanying drawings, in which:

Figure 1 is a side elevation of my improved spark plug.

Figure 2 is a longitudinal sectional view of'the same taken on theline'a'2 of Figure 1. I

Myimprovedspark plug comprises a casing 10,-the upper endof :which' isprovided with a hexagonal 'nut "11, and the lower end of whichisprovided with a screw threaded portion 12.

The casing lOis-provided with a centrally arranged cylindrical opening13. *The upper end of the opening 13 is provided witha screw threadedportion 14:,tllQlOlVQI' end of the casing is provided with a cylindircalopening 15 of a slightly less diameterthan the opening 13 so that aslight'inclined 'inwardly extending shoulder 16 is provided. The lowerend of the opening 15 is provided with an inwardly extcnding flange l7,the inner edges of which form an opening 18. Theportion 12 is ofstandard diameter and provided with standard thre-ads.

The insulatingineniber'19 of my improved spark plugis perferably formedof ,aseries of discs of mica and laid adjacent to each other and boundtogether by means ofcentrally located conductor rods-20.

These rods 20 are spaced a slight-distance apart and have their upperends screw threaded and extending througha plate 21, and each providedwith anut 22.

The plate 21 is formed il-shaped so that the upper portion of saidmember 21 lies above the nuts 22 and is pro videdwitha terminal screw23. Abe said sci'ew'is-provided with the usual terminal nut 2% so anranged that connection inay be made between a suitable conductor wireand the plate'Ql.

The lower ends of the rods :20 extend downwardlythrough the lower end ofthe insulating member 19, and are provided with collars 25 which restadjacent tothelower end of said member 19,thereby providing meanswhereby the discs of said -member may be rigidly clampedbetween thecollars 25, andtlie plate 21 forming the ncmber 19 into a rigidinsulator.

The central portion 26 of the insulator l9 is formed cylindrical and ofa diameter slightly less than the diameter of the opening 13 anddesigned to rest in said opening when in its normal position.

The upper end of the member 19 is formed slightly conical, the lower endof the conical member being of a less diameter than the member 26 toform a shoulder 27.

The shoulder 27 and the adjacent portion of the member 19 is providedwith a conical sleeve 28 having an outwardly extending flange 29, theflange 29 being designed to rest on the shoulder 27, and the portion 28being designed to snugly fit the lower end or" the conical portion. 7

A screw threaded bushing 30 is provided and designed to coact with thescrew threadedportion 14. The said bushing is provided with a hexagonalnut 31 and with a conical opening 32 designed to fit the outer surfaceof the member 28, while the inner end of the bushing 30 rests againstthe flange 29. The opening in the bushing, however, is loose enough soas to permit the said bushing to rotate freely on the sleeve 28. Thisforms means whereby theinsulator may be secured in the casing as willhereinafter be made clear.

Adjacent to the lower end of the cylindrical portion 26, I have provideda smaller cylindrical portion 33, and adjacent to the lower end or thecylindrical portion 33, I have provided a downwardly extending conicalportion 34, the upper end of the conical portion 34 being of lessdiameter than the portion 33 to form an annular shoulder 35.

The diameter of the portion 33 is slightly less than the diameter of theopening 15, while the diameter of the lower end of the conical portion34 is of a diameter substantially equal to the diameter of the open-Ving 18.

Mounted upon the portion 33, I have provided a shell 36 of thin sheetmetal having a number of annular and outwardly extending beads 37, andat its lower end an annular and inwardly extending flange 38. The inneredge of the flange 38 is designed to Test against and overlap the lowerend of the insulating member 19.

The space between the shell 36 and the conical portion 34 is filled withasbestos or some other insulating, heat-resisting material 39. Inassembling the shell 36 the member 39 is placed adjacent to the portion34,

then the shell 36 is placed over the member 39 and the said casingsqueezed longitudinally onto the member 33. This will cause the member39 to be packed and squeezed to a very condensed condition so as topositively engage the ends of the .discs torming the portion 34, andthereby form an oil tight joint to prevent the oil from seeping betweenthe discs.

After the shell 36 has been squeezed into position, the .upper edge ofsaid shell is spun into the cylindrical portion 33, as s own at 40, soas to prevent the said shell from moving out of position due to the expansion of the material within.

By this arrangement, it will be seen that I have provided an insulatingmember comprising the member 19, the shell 36 and the packing 39 in aunitary form whichmay be removed or placed in the casing 10 when sodesired. The beads 37 are of such diameter that they will be squeezedinto position as the member 19 is moved downwardly into the opening 15,and as they engage the in clined shoulder 16, thereby forming a tightjoint between the beads and the wall of the opening 15 to prevent oilfrom entering the space between the portions 26 and 33 and the walls ofthe opening 13. 7

To further assist in preventing the oil from working upwardly betweenthe insulating member and the casing 10, I have provided a packingwasher 41 which is similar to those used in spark plugs.

The packing 41 is placed between the flange 38 and the flange 17. NVhenthe bushing 30 is screwed into the casing 10 the said flanges will bemoved toward each other and engage the packing 41, thereby forming atight joint.

By making the bushing 30 loosely mounted on the sleeve 28, the saidbushing may be screwed into position and the insulator clamped withoutrotating the said insulator and destroying the contact between thepacking 41 and the adjacent flanges, the beads 3? and the adjacent wall.By forming the sleeve28 so that it tightly fits the member 19, theportion 28 of the said sleeve will be made to carry a portion of theforce applied by the bushing '30, and to distribute the said force to alarge number of discs of the member 19 rather than applying all of thepressure to the shoulder 27 as has been done heretofore. lVhen all thepressure is applied to the shoulder 27, it causes the disc adjacent tothe bushing 30 to be sprung downwardly and a fracture or opening willresult between the lower end of the conical portion and the upper end ofthe cylindrical portion 26. By providing the conical sleeve 28 thepressure is applied substantially uniform to all of the discs and nofracture will result.

The lower ends of the members 20 are curved slightly inwardly towardeach other to form a spark gap. A ground member 42 is provided, thelower end of which is spaced member of which dinary spark plug as I findit gives better results.

By this arrangement, it will be seen that I have provided a spark plug,the insulating may be formed of mica or similar material and so arrangedthat oil or similar substances will not enter the space between thediscs. The insulating member may be easily and quickly removed from thew casing when so desired, for cleaning and renewing. It will also beseen that I have provided improved means whereby the said insulator maybe effectively and efliciently secured in the casing without destroyingor breaking down the discs of the insulating member.

I claim as my invention.

1. A spark plug comprising a casing having a cylindrical opening at itscentral portion, the inner end of said opening being provided with aninwardly extending flange, an insulator formed of a series of adjacentand transversely arranged disks, said insulator being provided with anenlarged cylindrical portion designed to fit the upper end of theopening of said casing having an upwardly and outwardly extending endand a downwardly extendinocylindrical portion, the lower end of whici isformed conical, a packing member for the conical portion of saiddownwardly extending end, means secured to the downwardly extendingcylindrical portion for securing said packing in position, means forsecuring said insulator member within said casing, a conductor memberfor said insulator, and a ground member for said casing placed inoperative relation with each other.

2. A spark plug comprising a casing having a clyindrical opening in itscentral portion and a smaller cylindrical opening adjacent to one end,the inner end of said smaller opening being provided with an inwardlyextending flange, the outer end of said larger cylindrical opening beingscrew threaded, an insulator formed of a series of adjacent andtransversely arranged disks, said insulator being provided with acylindrical portion designed to fit the larger opening of said casing,the lower end of said insulator being provided with a smallercylindrical portion and a smaller conical portion, a packing member forcovering the last said conical portion and means for securing saidpacking member thereto, a conductor extended longitudinally through saidinsulator, a terminal screwed to the upper end of said conductor, aground conductor in operative relation with the first said conductor, ascrew threaded bushing designed to coact with the screw threaded portionof said casing and to secure the insulator in position.

3. A spark plug comprising a casing having a cylindrical opening at itscentral portion and a smaller cylindrical opening adjacent to one end,the inner end of said smaller opening being provided with an inwardlyextending flange, the outer end of said larger cylindrical opening beingscrew threaded, an insulator formed of a series of adjacent andtransversely arranged discs, said insulator being provided with acylindrical por tion designed to fit the larger opening of said casing,and with a conical upwardly extending end, a sleeve for said upwardlyextending conical portion, a bushing for said sleeve, a conductorextending longitudinally through said insulator, a terminal screw forthe upper end of said conductor, the lower end of said insulator beingprovided with a smaller cylindrical portion, and a smaller conicalportion, a packing member for the last said conical portion, and meansfor securing said packing member thereto, a packing ring between thelower end of said insulator member and the annular flange of saidcasing, a ground conductor in operative relation with the first saidconductor.

4. A spark plug comprising a casing, an insulator member mountedtherein, a double conductor arranged longitudinally through the centerof said insulator having the lower ends of its members bent slightlytoward each other, a collar on each of said members spaced apart anddesigned to rest against the lower end of said insulator, the spacing ofsaid collars being less than the spacing between the downwardlyprojecting end, a terminal at the upper end of said insulator memberbeing connected to both of said conductors, means for securing saidinsulator in said casing, and a ground conductor in operative relationwith the first said conductors.

5. A spark plug, a casing having a cylindrical opening at its centralportion and a smaller cylindrical opening adjacent to one end, the innerend of said smaller opening being provided with an inwardly extendingange, an insulator formed of a series of adjacent and transverselyarranged disks, said insulator being provided with a cylindrical portiondesigned to fit the larger opening of said casing and a smaller upwardlyextending end, the lower end of said insulator being provided with asmaller cylindrical portion and a smaller conical portion, a packingmember for the last said conical portion, means for securing saidpacking member thereto, a packing ring between the lower end of saidinsulator member and the annular flange of said casing, longitudinallythrough said insulator, a ground conductor in operative relation withthe inwardly extending end of the first said conductor, means fordetachably securing the insulator member within said casing.

Des Moines, Iowa, September 2, 1921.

WILLIAM CHRIS THOMA.

a conductor extended

